This invention relates in general to noise reduction structures for use in vehicle driveshaft assemblies. In particular, this invention relates an improved noise reduction structure that has a passageway or other opening formed therethrough for providing a vent between a vent opening formed in an end fitting secured to one end of a driveshaft tube and interior chambers defined within the driveshaft tube when the noise reduction structure is disposed therein.
Torque transmitting shafts are widely used for transferring rotational power between a source of rotational power and a rotatably driven mechanism. An example of a torque transmitting shaft is a driveshaft tube used in a vehicle driveshaft assembly. The driveshaft assembly transmits rotational power from a source, such as an engine, to a driven component, such as a pair of wheels. A typical vehicle driveshaft assembly includes a hollow cylindrical driveshaft tube having an end fitting secured to each end thereof. Usually, the end fittings are embodied as end yokes which are adapted to cooperate with respective universal joints. For example, a driveshaft assembly of this general type is often used to provide a rotatable driving connection between the output shaft of a vehicle transmission and an input shaft of an axle assembly for rotatably driving the vehicle wheels. Traditionally, driveshaft tubes were made from steel. More recently, aluminum driveshafts have been developed because of their lighter weight.
One problem encountered by all types of driveshaft assemblies is their tendency to produce and transmit sound while transferring the power of the engine to the axle assembly. It is known that any mechanical body has a natural resonant frequency. This natural resonant frequency is an inherent characteristic of the mechanical body and is based upon many factors, including its composition, size and shape. The natural resonant frequency is made up of many sub-frequencies, often referred to as harmonics. As the vehicle is operated through its normal speed range (i.e. from 0 mph to about 80 mph), the rotational velocity of the driveshaft assembly changes (i.e. from 0 rpm to about 5000 rpm). As the rotational velocity of the driveshaft changes, it passes through the harmonic frequencies of the body's resonant frequency. When the rotational velocity of the driveshaft passes through these harmonic frequencies, vibration and noise may be amplified since the two frequencies are synchronized and the rotational energy of the driveshaft is converted into vibration and noise. This noise can be undesirable to passengers riding in the vehicle. Thus, it would be advantageous to deaden or reduce the sound produced by a vehicle driveshaft assembly in order to provide the passengers with a more quiet and comfortable ride.
Various attempts have been made to deaden the sound produced by vehicle driveshaft tubes. One general direction that many of these attempts have followed is to place a noise absorbing/deadening structure within the driveshaft. For example, one attempt involves disposing a hollow cylindrical cardboard insert inside an aluminum driveshaft tube to deaden the sound. However, the cardboard insert required external rubber ribs to prevent it from sliding inside the aluminum driveshaft tube. As a result, the cardboard insert is relatively complicated and expensive to employ. It is also known to place a solid noise reduction structure within the driveshaft tube to absorb noise and vibration. A typical noise reduction structure is a generally cylindrical member having a predetermined length which is disposed within a driveshaft tube in a press fit relationship with the inner surface of the driveshaft tube. Typically, the noise reduction structure is positioned within the driveshaft tube at a location where the amplitude of a standing wave caused by the reflection of the sound waves back and forth along the driveshaft tube is at its maximum value. If more than one noise reduction structure is disposed therein, the first noise reduction structure is located a certain distance inward from one of the ends of the driveshaft tube and the remaining noise reduction structures are then spaced apart, typically at equal intervals. As noted previously, the typical driveshaft assembly further includes an end fitting secured to each end of the driveshaft tube.
In any hollow driveshaft assembly, air can become trapped within its internal space when the two end fittings are secured to the hollow driveshaft tube. In the past, this space was vented by forming a vent opening in one of the two end fittings secured to the opposite ends of the driveshaft tube. The vent opening prevents an undesirable vacuum or pressure from occurring within the driveshaft tube. However, the use of one or more solid noise reduction structures within the driveshaft tube prevents some of the internal spaces from being vented through the vent opening. If a noise reduction structure is disposed within the driveshaft tube, the interior of the driveshaft tube is divided into two chambers, one of which is vented and one of which is not. Similarly, if multiple noise reduction structures are disposed therein, the interior of the driveshaft tube is divided into several chambers, with only one of these chambers being vented. While a vent opening could be formed through each of the end fittings, it is preferable to avoid the time and expense involved with such an additional manufacturing step. In addition, this step would not fully vent the interior of the driveshaft tube if two or more noise reduction structures are disposed therein. Thus, it would be desirable to provide an improved noise reduction structure that insures that each of the interior chambers of the driveshaft tube is properly vented during use.